Valproic acid promotes mitochondrial dysfunction in primary human hepatocytes in vitro; impact of C/EBPα-controlled gene expression

Valproic acid (VPA) is a frequently prescribed anti-epileptic drug which is known to cause liver toxicity and steatosis through mitochondrial dysfunction. Nevertheless the mechanisms underlying these adverse effects are incompletely understood. In this study, we determined the effect of relatively short (3 h) or prolonged (72 h) exposure to VPA on mitochondrial function in primary human hepatocytes (PHHs). While 3 h VPA exposure did not affect oxygen consumption rates (OCRs) in PHHs, prolonged exposure (24–72 h) significantly reduced basal and maximal OCRs. Given that in particular prolonged VPA exposure is required to cause mitochondrial dysfunction, we investigated gene expression data after VPA exposure for 24, 48, 72 h and 72 h VPA followed by a 72 h washout period. We were able to reduce the comprehensive gene expression changes into a more comprehensible set of 18 TFs that were predicted to be persistently activated after 72 h of VPA exposure. Lentiviral knock-down of one of the candidate TFs, C/EBPα, partly rescued VPA-induced mitochondrial dysfunction. Furthermore, RNA-Seq analysis of shC/EBPα and shGFP control PHHs identified 24 genuine C/EBPα target genes that are regulated in response to prolonged VPA exposure in PHHs. Altogether this provides new insights on the involvement of C/EBPα in driving VPA-induced mitochondrial dysfunction in human liver cells. This hub gene, with its downstream regulators involved in this deregulation, thus represent potential new biomarkers for VPA-induced mitochondrial dysfunction.

The exposome in practice: Design of the EXPOsOMICS project

EXPOsOMICS is a European Union funded project that aims to develop a novel approach to the assessment of exposure to high priority environmental pollutants, by characterizing the external and the internal components of the exposome. It focuses on air and water contaminants during critical periods of life. To this end, the project centres on 1) exposure assessment at the personal and population levels within existing European short and long-term population studies, exploiting available tools and methods which have been developed for personal exposure monitoring (PEM); and 2) multiple "omic" technologies for the analysis of biological samples (internal markers of external exposures). The search for the relationships between external exposures and global profiles of molecular features in the same individuals constitutes a novel advancement towards the development of "next generation exposure assessment" for environmental chemicals and their mixtures. The linkage with disease risks opens the way to what are defined here as 'exposome-wide association studies' (EWAS).

Inter-laboratory study of human in vitro toxicogenomics-based tests as alternative methods for evaluating chemical carcinogenicity: a bioinformatics perspective

The assessment of the carcinogenic potential of chemicals with alternative, human-based in vitro systems has become a major goal of toxicogenomics. The central read-out of these assays is the transcriptome, and while many studies exist that explored the gene expression responses of such systems, reports on robustness and reproducibility, when testing them independently in different laboratories, are still uncommon. Furthermore, there is limited knowledge about variability induced by the data analysis protocols. We have conducted an inter-laboratory study for testing chemical carcinogenicity evaluating two human in vitro assays: hepatoma-derived cells and hTERT-immortalized renal proximal tubule epithelial cells, representing liver and kidney as major target organs. Cellular systems were initially challenged with thirty compounds, genome-wide gene expression was measured with microarrays, and hazard classifiers were built from this training set. Subsequently, each system was independently established in three different laboratories, and gene expression measurements were conducted using anonymized compounds. Data analysis was performed independently by two separate groups applying different protocols for the assessment of inter-laboratory reproducibility and for the prediction of carcinogenic hazard. As a result, both workflows came to very similar conclusions with respect to (1) identification of experimental outliers, (2) overall assessment of robustness and inter-laboratory reproducibility and (3) re-classification of the unknown compounds to the respective toxicity classes. In summary, the developed bioinformatics workflows deliver accurate measures for inter-laboratory comparison studies, and the study can be used as guidance for validation of future carcinogenicity assays in order to implement testing of human in vitro alternatives to animal testing.

Intake of butylated hydroxyanisole and butylated hydroxytoluene and stomach cancer risk: results from analyses in the Netherlands Cohort Study

Both carcinogenic and anticarcinogenic properties have been reported for the synthetic antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). The association between dietary intake of BHA and BHT and stomach cancer risk was investigated in the Netherlands Cohort Study (NLCS) that started in 1986 among 120,852 men and women aged 55 to 69 years. A semi-quantitative food frequency questionnaire was used to assess food consumption. Information on BHA or BHT content of cooking fats, oils, mayonnaise and other creamy salad dressings and dried soups was obtained by chemical analysis, a Dutch database of food additives (ALBA) and the Dutch Compendium of Foods and Diet Products. After 6.3 years of follow-up, complete data on BHA and BHT intake of 192 incident stomach cancer cases and 2035 subcohort members were available for case-cohort analysis. Mean intake of BHA or BHT among subcohort members was 105 and 351 microg/day, respectively. For consumption of mayonnaise and other creamy salad dressings with BHA or BHT no association with stomach cancer risk was observed. A statistically non-significant decrease in stomach cancer risk was observed with increasing BHA and BHT intake [rate ratio (RR) highest/lowest intake of BHA = 0.57 (95% confidence interval (CI): 0.25-1.30] and BHT = 0.74 (95% CI: 0.38-1.43). In this study, no significant association with stomach cancer risk was found for usual intake of low levels of BHA and BHT.

Influence of smoking behavior in relation to plasma retinol and alpha-tocopherol on sister chromatid exchanges in human peripheral blood lymphocytes

The present study was undertaken to evaluate the contribution of various individual characteristics and lifestyle factors on sister chromatid exchange (SCE) frequencies in human peripheral blood lymphocytes (PBLs). These also included associations between plasma retinol and alpha-tocopherol and SCE frequencies. The study population consisted of 50 healthy, smoking and nonsmoking, male and female volunteers, ages 22-49. SCE frequencies in PBLs were significantly higher in smokers than in nonsmokers. SCE frequencies correlated with variables of smoking habits and history, with the number of pack-years smoked correlating most strongly (r = 0.501; P < 0.001). Inverse but nonsignificant correlations were observed between plasma retinol and alpha-tocopherol levels and SCE frequencies in PBLs. In addition, with the use of multiple regression analysis, significant associations were found with age and possible occupational exposure after adjustment for smoking habits (r2 = 0.428; P = 0.0001). For males (n = 20), SCE frequencies were found to be associated significantly with the number of cigarettes smoked per day and possible occupational exposure (r2 = 0.485; P < 0.01). SCE frequencies in PBLs of females (n = 30) were associated positively with the number of pack-years smoked and age, and significantly inversely correlated with plasma alpha-tocopherol concentrations (r2 = 0.586; P = 0.0001). After exclusion of possible occupationally exposed persons (n = 8) from the study population and adjustment for the effects of age and smoking behavior, a weak inverse correlation was found between plasma alpha-tocopherol and SCE frequencies (r = -0.286; P = 0.0732).(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of 6-thioguanine-resistant human peripheral blood lymphocytes using 5-bromodeoxyuridine labeling in combination with immunocytochemical staining

Measurement of frequencies of 6-thioguanine-resistant (TGr) human peripheral lymphocytes may contribute to quantitative genetic risk assessment in occupationally or environmentally exposed human populations. A simple procedure for the detection of TGr human peripheral blood lymphocytes was developed in our laboratory, using whole blood culturing and 5-bromodeoxyuridine (BrdU) labeling in combination with immunocytochemical staining. Modifications of the procedure designed to reduce the false positive effects of spontaneously cycling lymphocytes (phenocopies), and to optimize duration of BrdU labeling and the culturing period, were evaluated. A standard procedure was developed which applied 24 h cold storage of the diluted heparinized blood (1:10, v:v in RPMI 1640 medium) at 4 degrees C to reduce the effect of spontaneously cycling lymphocytes, and whole blood culturing in RPMI 1640 complete medium with stimulation of T lymphocytes using phytohemagglutinin (PHA), selection of TGr lymphocytes by adding TG to a final concentration of 2 x 10(-4) M and, after 24 h of incubation, labeling of TGr lymphocytes with 2.5 x 10(-5) M BrdU during 16 h. Using this standard procedure, frequencies of TGr cells in 45 healthy individuals (aged 21-64) were observed to range from 0.3 to 229.8 x 10(-6), with a mean variant frequency (VF) (+/- SD) of 136 x 10(-6) (+/- 35.8). After exclusion of the one extremely high value of 229.8 x 10(-6), mean VF was 8.7 x 10(-6) (+/- 14.1). A significant inverse correlation was found between logVF and the labeling index of control cultures (LIc), indicating that cultures with low LIc tend to yield higher VF.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological effects of short-term feeding to rats of repeatedly used deep-frying fats in relation to fat mutagen content

The effects of short-term feeding of mutagen containing, heated deep-frying oils on urinary and faecal mutagenicity, plasma clinical biochemical parameters, peroxidative effects and cell proliferative indices in the gastro-intestinal tract were determined in rats. Repeatedly used frying oils [a saturated fatty acid-rich coconut oil (CO) and a polyunsaturated fatty acid (PUFA)-rich (greater than 60% PUFA) vegetable frying oil (PO)] were administered to groups of seven rats at a level of 10% (by weight) in the diet for 4 wk; control groups were fed equal amounts of the unheated oils. Both heated oils showed direct-acting mutagenicity to Salmonella tester strain TA97; heated PO was also mutagenic to strain TA100. Both heated CO and heated PO contained detectable amounts of thiobarbituric acid-reactive substances (TBA-RS). In heated PO, hydroperoxides of linoleic acid were also present. In groups fed heated oils the mutagenicity of urine and faeces to strain TA97 was not found to be increased in comparison with the control groups. Faecal mutagenicity to strain TA100 was also unaffected by consumption of heated oils. Urinary excretion of TA100 mutagens was significantly increased in rats fed heated PO. Plasma alkaline phosphatase activity was clearly raised in rats fed heated PO, in comparison with rats fed unheated oils or heated CO. In addition, other clinical biochemical plasma parameters showed a tendency to be increased in rats fed heated PO, indicating hepatic and renal cellular toxicity. Urinary and faecal excretion of thiobarbituric acid-reactive substances (TBA-RS) were also slightly, but not significantly, increased in rats fed heated PO. Feeding heated CO to rats did not result in increased plasma enzyme activities and excretion of TBA-RS, nor in increased cell proliferation in gastro-intestinal tissues. Cell proliferation of the oesophageal tissues were slightly, but significantly, increased in rats fed heated PO, in comparison with the group fed unheated PO. Tissues of the glandular stomach and colon/rectum did not show significantly enhanced cell proliferation in the group fed heated PO. The results obtained in this study indicated that consumption of heated oils containing TA100 mutagens and oxidation products of linoleic acid produced indications of cellular damage to liver and kidneys, and increased urine mutagenicity, as well as enhanced cell proliferation in the oesophagus.

Mutagenicity of deep-frying fat, and evaluation of urine mutagenicity after consumption of fried potatoes

Mutagen formation during deep-frying was evaluated using standard frying conditions. Portions of pre-fried, sliced potatoes were fried in a commercial brand of hydrogenated vegetable frying fat, which was used repeatedly and for a prolonged period of time. Concentrations of polar oxidation and degradation products, and of dimeric and polymeric triglycerides, were found to increase in the frying fat as well as in fried potatoes with prolonged use of the fat. Thiobarbituric acid-reactive substances were detectable neither in the frying fat nor in the fried potatoes. Polar fractions of repeatedly used frying fat significantly increased the number of revertants in Salmonella typhimurium strain TA97 without S-9 mix. In the presence of S-9 mix mutagenic activity was reduced. As a consequence of ongoing formation of polar degradation and oxidation products, the mutagenicity of the fat increased after repeated use. Polar fractions of lipids extracted from commercially obtained pre-fried potatoes, as well as from fried potatoes, marginally increased the number of revertants in strain TA97 without S-9 mix. The mutagenicity of the lipid fractions of fried potatoes was not related to the heating time of the fat. Methanol extracts of fat-free residues of fried potatoes significantly increased numbers of revertants in strain TA97 after metabolic activation, which indicated that a different class of mutagens had been isolated. The mutagenicity of methanol extracts was not increased after either prolonged or repeated use of the fat. Urine samples of six healthy, non-smoking volunteers, collected during the 24 hr following consumption of portions of potatoes fried in repeatedly used fat, showed no increase in mutagenicity compared with control samples. Since the exact identity of mutagens formed during deep-frying, as well as their metabolic fate in man, is unclear at present, evaluation of possible adverse biological effects associated with consumption of fried foods will require strictly controlled metabolic studies.

Linoleic acid hydroperoxide concentration in relation to mutagenicity of repeatedly used deep-frying fats

A high-performance liquid chromatography procedure was developed to measure linoleic acid hydroperoxides (LAHPO) in 19 used, deep-frying fat samples that were screened for mutagenicity. The detection limit of the method was found to be 10 nmol of LAHPO/g of fat. In eight samples, LAHPO were not detected; levels in the other samples ranged from 17 to 267 nmol/g of fat. LAHPO were not detectable in unused hydrogenated frying fat samples. Concentrations of LAHPO correlated positively with mutagenicity to Salmonella tester strains TA97 and TA100, in presence of S9 mix only; coefficients of correlation were, respectively, r=0.48 (p less than 0.05) and r=0.24 (n.s.). Without metabolic activation no significant associations or secondary autoxidation products of linoleic acid generated in presence of liver S9 mix may contribute to mutagenicity of some of the used deep-frying fat samples.

Assessment of mutagenic activity of repeatedly used deep-frying fats

Mutagenic activity of repeatedly used deep-frying fats was evaluated in relation to chemical characteristics. Deep-frying fat samples were collected from local restaurants and snack bars after sensory indication of abuse. A total of 20 deep-frying fat samples and 2 unused control fat samples was tested. Fat samples were fractionated into non-polar and polar compounds by column chromatography. Amounts of polar compounds obtained ranged from 2% (by weight) for unused fat to 44% for used deep-frying fat. Levels of di- and polymeric triglycerides (DPTG) were determined using gel-permeation chromatography. DPTG concentrations of 13 used deep-frying fat samples exceeded the threshold level of 10% above which fats are rejected for use. In addition thiobarbituric acid-reactive substances (TBA-RS) were measured. Amounts of TBA-RS were just above detection levels for most fat samples. Five used fat samples, however, contained relatively high concentrations of TBA-RS, ranging from 82 to 177 nmoles malondialdehyde/g. Non-polar and polar fractions were screened for mutagenic activity using the Ames mutagenicity assay. Mutagenic activity was found predominantly in polar fractions at doses higher than 1 mg/plate in strains TA97, TA100 and TA104, variously with and without metabolic activation. The highest number of mutagenic samples was detected by strain TA97, which appeared to be most sensitive. Some samples exhibited toxic effects. Chromatography blanks, consisting of solvents processed according to the same procedures as used for fat samples, were not mutagenic. Mutagenic activity was also detected in polar material obtained from unused frying fat. Non-polar fractions of unused frying fats showed no mutagenicity. A frying experiment carried out under laboratory conditions indicated that during repeated and prolonged use of deep-frying fat mutagenic polar substances were formed. Fat samples taken after 20 and 40 h of frying contained increasing amounts of polar compounds. Mutagenic activity was highest after 20 h of frying but was slightly decreased after 40 h of frying. At this stage, however, mutagens also appeared in the non-polar fraction. Mutagenic activity of polar fractions of used deep-frying fats in strain TA97 was positively correlated with levels of TBA-RS, which may indicate the involvement of lipid oxidation products in mutagenicity of used deep-frying fats. No significant correlations were found with other chemical characteristics. In the process of deep-fat frying numerous degradation products are formed, which may include mutagenic heterocyclic amines and other pyrolysates.(ABSTRACT TRUNCATED AT 400 WORDS)